BACTERIA ON THE SURFACE OF PLANTS. 33 
Haven Mectalf found a non-pathogenic red Schizomycete associated almost constantly 
with the Piricularia disease of rice in South Carolina. Its habitat is undoubtedly the surface 
of the rice plant. 
In experimenting with peas Mrs. Bitting found that fresh peas taken from the pods 
under sterile precautions always failed to contaminate culture-media, and that this condi- 
tion of sterility persisted for a number of hours (fig. 2), but not for days. Peas from pods 
picked for a longer time than 18 hours, often infected cultures and gave, with lapse of time, 
an increasingly large number of contaminations, showing that the surface bacteria were 
able to enter the unopened pods and contaminate the seeds (verbal communication). 
In his physiological experiments with germinating seeds of Vicia faba, etc., where 
surface sterility was necessary, Harley H. Bartlett obtained it in many instances by care- 
fully slipping the soaked seeds out of their seed coats. 
Diiggeli, in Ziirich, studied this subject quantitatively as well as qualitatively. He 
experimented with about 40 species of plants, some of which were sampled repeatedly. 
He selected sound parts—seeds, fruits, stems, leaves, and whole plants in case of certain 
seedlings grown in sterile sand. A great many gelatin poured-plates were made, and his 
detailed studies involved an enormous amount of labor. 
In general he found great numbers of bacteria on the surfaces of plants. Only very 
exceptionally did he fail to obtain them, but occasionally they were few. Shaking the stem 
or other part in water for ten minutes did not remove all of them. He therefore made his 
comparative tests by grinding up a measured portion or weighed quantity of the material, 
some of which then served for the test. 
The same organisms were found on seeds, seedlings, and mature plants. In general 
there was a poverty of species. A few species occurred on so many plants and over and 
over again so abundantly that he was forced to regard them not as accidental occurrences, 
i.¢e., not as organisms which had settled down out of the air, but as true epiphytes peculiar 
to the surface of the plants. 
The most common form was a motile gelatin-softening yellow schizomycete, named 
by him Bacterium herbicola aureum, but said to be the same as the Bacillus mesentericus 
aureus isolated by Winkler from the surface of plum leaves. This form occurred on a 
great variety of plants, often to the exclusion of other species. For example, of 55 samples 
of seeds examined, 21 bore this organism, practically to the exclusion of all others, while 
only 7 samples were free from it. This organism is a short, actively motile, non-spor- 
iferous rod, single or paired, 1 to 3 x 0.6 to 0.7, forming characteristic zoologee. No 
statement is made respecting number or attachment of flagella. It is gold-yellow on 
gelatin and agar (gray at first), and gold-yellow on potato. Milk remained unchanged or 
was curdled by acid, some acid formed also in the bouillon. Urea was not converted into 
ammonia. Nitrates were reduced, and there was a strong indol reaction in bouillon 6 days 
old. The organism is aerobic and probably facultative anaérobic. Growth was good the 
whole length of the stab, but ordinarily no gas was formed from grape-sugar. It does not 
stain by Gram. Growth and pigmentation on agar streaks was more rapid at 37° C. than 
at 30° C. 
A second common form was a liquefying, green-fluorescent species, identified by him 
as Bacillus fluorescens (Fliigge). A third species, Bacterium putidum (Fliigge) L. & N. 
was also found widely distributed. According to Diiggeli these three species are the 
dominating ones on the surfaces of plants. 
A fourth common species produces a manganese red pigment on potato. This is 
called Bacterium herbicola rubrum. It was feebly motile and did not liquefy gelatin. Other 
sorts were much less abundant. Of these he names: Bacillus mesentericus, B. vulgatus, 
B. megaterium, and B. colt, 
